Carrier signaling system



E. l. GREEN CARRIER SIGNALING SYSTEM I July 24, 1928.

Filed Deo. 3Q, 1925 A TTORNE Y 1%. SQSM mg Patented `July 24,` 1.928.-

lUNITED STATES PATENT OFFICE.:

'ESTILL I. GREEN, OF EAST ORANGE, NEW JERSEY, ASSIG-'NOR 4'10 AMERICANTELE- PHONE ANI) TELEGBAPH COMPANY, A CORPORATION OF NEW YORK.

Calmann SIGNALING SYSTEM;

'- Application nica December so, 192s. semi iro.- 78,455.

the lowest frequency channel (which has the least attenuation) below theoverload point of the repeaters. This equalization of the yaviouschannels is ordinarily carried out by means of networks which reduce allchannels to the same level at each repeater point. This practice ofreducing t-he volumes of all the channels to substantially the sainelevel, which in practice is the level ofvthe'highest frequency channel,is highly ineiicient because of the waste of energy of the lowerfrequency channels.

This invention resides in a method and means for equalizing thetransmission equivalents of a plurality of channels of differentfrequencies transmitted over or through `a common transmitting medium,which method consists in inverting the channel fre quencies in alternaterepeater'sections.` Such,

. method has distinct advantages over. the

Vfinethod heretofore employed in that the present method equalizes thechannels with respect to their frequency of transmission,

which is the real difference between the channels, rather than withrespect to attenu@ ation, which is only a characteristic of thefrequency. The equalization of the channels with respect to frequencyeffectively provides equalization with respect to all the factors whichfare a function of frequency.

such as gain, noise, cross-talk, attenuation variations and othersimilar functions This invention will be clearly understood from thefollowing description when read in connection with the attached drawingof which Fig; 1. shows schematically a form of embodiment of theinvention -in which the range of frequencies to be transmitted over thecommon medium 'is such asto permit the carrying out of the inventionbywdividing l' the channels into only two groups; and Fig.

2 shows .schematically an' arrangement `fol' handlinga greater number ofgroups. 'In

the drawing the line L1, which represents the medium over which aplurality of channels is transmitted, ismade upv of a plurality ofsections designated X, Y and Z, -thc ad]acent sections being connectedthroufh the repeaters, such as Nos. 1 and 2, and tie said,line beingterminated at its ends by a ool station, such'as A. While station A isrepresented as beingr adapted onlyfor the transmission of signals, it isto be understood, of course, that it may be readily adapted both fortransmission and-reception in a manner` that is well understood by thosefamiliar with the art. Station A com rises a'pluiality of branchcircuits of whic sirare shown in the drawing, but the number may varydepending upon the' number of channels of communication. VEach of thebranch circuits comprises a transmitter, a's indicated by 7 to 12,asource of carrier oscillations, asindicated by 13 to 18, a modulatingdevice, as

indicated by 19 to 24, and a filter, such as is indicated by 25 to 30,The transmitters 7 to 12 may be any device by means of whicha-modulating current is impressed .upon the input side of themodulators'to modulate the carrier current from the oscillators. Eachoscillator is designed` and adjusted to produce a frequency differingfrom that of the other oscillators. Y

Considering, lfor example, branch circuit N o. 1, if the transmit-ter 7is designed to impress a frequency range from z ero to 4 kilocycles uponthe input side of the modulator 19 and the oscillator is adjusted toproduce kilocycles,the output of the modulator (assuming that it were ofthe` type to suppress the carrier frequency) would comprise two bands,one ranging from 100 to 104 kilo- 'cycles and the lother ranging. from100 to 96- kilocycles. Assuming single side band transmission, thefilter 25 would be 'adjusted to pass only one band, as, for example,that

representing 100 to 104 kilocycles. In like manner, each of the othervbranch circuits would produce a band of oscillations based.

upon its individual carrier frequency. Thus circuit No. 2 would producethe` band 105 to 109-kilocvcles, and the'third'circuit a band 11o to iiikiiocyeis. Circuits 4 tez/6, in-

clusive, would produce three channels'ranging from 116to' 130kilocycles. f .Y All of these frequencies would be impressed juponY theline L, and transmitted m to the repeater No. 1, which comprisesy thefilters 31 and 32, the former passing the frequencies 100 to 114kilocycles, and the latter the frequencies 116` to 130 kilocycles.

-These filters are connected with the input 36 and 37, respectively. Theoutput circuits aol of the amplifiers are connected with thel section Yof the line which extends to repeater No.J 2. This repeater ispreferably similar to repeater No. 1,' and upon the drawing the sameparts have at repeater No. 2 been givencthe same numerals primed.

.Repeater No. 2 is connected with section Z of the line, which mayextend to another. repeater or to a terminal station having a pluralityof branch circuits, such as A, adapted to receive the channels and todemodulate the frequencies and produce the signal freqency upon eachchannel. n .n

The principle involved in this invention yconsists in splitting up the nchannels into groups at each repeater station and modulating each groupby a carrierv frequency equal to the sum of the maximum and the mini mumtransmitted frequencies. This will be made clear by vconsidering aspecific case, such as that involved in the transmission of sixchannels, representing a frequency range of from'lOO to 130 kilocycles.These frequencies,'which are impressed upon section X of the line, willbe attenuated as the result'of such transmission, the higherfrequencies, of course, suffering greater attenuation than the lowerfrequencies. It will there ore be apparent that if at the repeaterstation No. 1 these frequencies lare inverted before transmission oversectionl Y of thel line,'the frequencies having greatest attenuation insection X will have least attenua'' tion in's'ection Y, and vice versa..This desirable result is effected in the following manner:

4 The frequencies which are present in the channels ofl transmission are,divided at repeater No. 1 into two groups by means of the filters 31and 32. Thus filter 31 transmits'through it the frequencies of 100 to114:

kilocycles, representing channels 1 to 3, and

filter 32 transmitsv frequencies. 116 to 130 kilocycles, representingchannels @to 6, If the intermodulation between frequencies of a group is.not'.serious,' it will always be possible to effect the inversion of.the frequencies by employing only two groups at each repeater. In casethe intermodulation cannot `be neglected, the groups must be so'chosenthat 4the intermodulation frequencies of any group `fall outsidethatl group and lowest frequency and f2 4the. highest frequency presentin the line L1, inversion of the frequencies may be effected withoutinterinodulation if 2f1 is equal to or greater than f2. Vhere thiscondition does not hold, it might be necessary to first divide thechannels into ,two groups and subsequently divide these groups intosmaller groups until such into two groups, 4as shown in the drawing.`

If these -groups be'beaten with the same carrier frequency which isequal `to the sum v of the lowest frequency in any group and thehighestfrequency in any group, and the difference frequency is selectedfrom each beating operation, it will be found that the frequencies ofthe channel have been inverted. Thus when .the group representing 100 to111,4 kilocycles, which may be termed the low frequency group in theline sect-ion X, is beaten with 230 kilocycles, the differencefrequencies, namely the group represented by 116 to 130 kilocycles, arethe same as the higher frequencies transmitted over the section X,'and.in like manner, when the group represented by 11G to 130 kilocycles isbeaten with 230 kilocycles andthe differ-- ence frequencies areselected, the resultant frequencies, namely, 110 to 114 kilocycles, arethe same as the frequencies of the lowest channels `transmitted oversection X. In

other words, the repeater has inverted the frequenciesof the channels.These frequencies are given the required amount of am plification by 38and 39 and transmitted over section Y to repeater No. 2. At the'latterlow frequencies in section X, become high v frequencies in section NY,and in like man` ner channels 4 to 6, which are of relatively highfrequencies in "section X, become low frequencies in section Y.l Bymeans of this frequency translat-ionl or inversion in a plurality ofsections of the line, the equivalents of the various channels may bemade sub- .lis

stantially the same.' With the frequency asl l sumed'in the foregoinginstance no interference-will be produced bythe intermodulation of thefrequencies`, `so that the inver-- sion'may be cared for by a singledivision of the channels into two groups. If, however, y thefrequencies-of the channels ranged, for

example, from 60 to 130kiloeyeles, it wouldV the inverted group. j,represents. the be necessary to-employ a greater number of 130` dividingprocesses to prevent intermodulation, such as is shown schematically inFig. 2. In such system' the line L, would be connected at repeater`1with two branches lhaving filters 41 and 42 capable of dividing theentire range of frequencies .into two groups,one extending from 60 to 94kilocycles, and the other from 96 to 130 kilo-l cycles. Since in thefirst group the frequency is more than half of 94, the inversion of thisgroup may be effected by dividing the group into two sub-groups, bymeans of the filters 43 and44 the former of which passes the frequenciesbetween 60 and 7 tkilocycles andthe latter the frequencies between 78and 94 kiloc'ycles. Since the lowest frequency of all the channels beingtransmitted over the system is l6() kilocyclesfandl the highest is 130kilocycles the beating 'frequency', employed is the sum of those fre--quencies. namely, 190l kilocycles. This is 'provided by an -oscillator47 which is connected with `the several branchcircuitsthrough filters orcircuits tuned to the beating frequency which permit-s the` passage ofthe beating vfrequency to the branch circuits butv prevents interactionbetween thosev circuits. The channels between 60 and 76 kilocycles passthrough the modulator 49 together with the beating frequency of 190kilocycles, and the difference frequencies resulting from modulation,which range from 130 tol14 kilocycles, are passed by the filter `51,amplified by the amplifier 53, and are passed to the line section Y. Inlike manner, the. group of frequencies extending from 78 to 94kilocycles will T be beaten with 190 kilocycles in the modulator 50, andthe difference frequencies, namely, those extending' from 112 tokilocycles, will be passed bythe filter amplified by the amplifier 54.vand passed to fthe line. It will be seen that the group of frequenciesthat was lowest in the frequency scale of all, the frequenciestransmitted over vthe line section X now occupies the highest positionin the frequency scale. Similarly thegroup ranging from 7 8 to 94kilocycles, which wasnext to the lowest. in transmission over section X,nowv voccupies the positionnext t'o the highest in the frequency scalein transmission over secy tion Y. In like manner the group offrequencies ranging from 96 to 130kilocyc1es, which is passed by thefilter 42,1is subdivided into two groups bythe filters 45 and46-and thefrequencies present in eachgroup are beaten with 190 kilocycles suppliedby the oscillator 47. The difference frequenciesI resulting frommodulation are passed by the filters 57 and 58 and amplifiedby-amplifiers 59 and 60, respectively. vItwill be seen that the groupranging fromv 114 to 130 kilocycles, passed by the filter 46, has, bythe process of modulation and selection, become the vlowest in thefrequency scale of all the groups transmitted overy section Y, occupyingthe Irange from 76 to 60 kilocycle-s. In like manner the group rangingfrom 9.6 to 112 kilocycles in transmission over section X, ranges from94 to 78 kilocycles in transmission over section Y.. The selectedfrequencies will be brought together againv and transmitted over sectionY to repeater No. 2 lwherein a similar process would restore thechannels to 'the frequencies possessed by them in section X. While'thefrequencies assumed for thepurpcse of describing this invention may seemto range fairly high,

such frequencies are not incapable of employment in telephone systemsland may be readily employed in carrier communicationv over powercircuits. It is, of course, obvious that any frequencies may be employedwithout exceeding'the scope of the invention.

While this invention has been disclosed as embodied in particularforms,it is ca` quency and -the f equencies in each group,`

and impressing u on the same transmitting medium the resultingfrequencies as selected. 2. The method of equalizing transmission of aplurality of carrier channels trans'- .mitted over or throughthe samemedium,

which consists in separating by filtering the said channels to form twogroups, one consisting of the higher frequencies and the other the lowerfrequencies, separately beating each group of 'frequencies by the samebeating frequency which equals the 4sum of. the lowest frequency and thef highest frequency present in the channels, selecting-the dlferencefrequencies resulting from reach beating operation, amplifying theselected,A

frequencies in each group, the degree ofamplification of the higherfrequencies being greater than thelower frequencies, and re-A combiningthe frequencies for transmission over`the said medium.

The method of equalizing of a plurality of carrier channels -transmittedover or through the same medium',

transmission p which consists in dividing the channels into two groups,changing the frequencies of the first group into those of the secondgroup, and

vvice versa, by beating separately the fre` quencies in the two groupsby afrequency equal to the sum of the lowest and highest frequencies inboth groups, amplifying the frequencieslresulting from the beating aopifrequencies of both. groups as thus trans-y lated, and impressing theamplified frequenc1es upon a common transmitting medium.

4. The method .of equalizing transmission separating the said channelsinto two groups,

by filtering, separately beating the groups of channels by a frequencywhich equals the' sum of the lowest and the highest frequencies in bothgroups, selecting the difference erations, separately amplifying tovdifferent degrees each'grou .of selected frequencies, and recombining te groups as-thus amplified.

5. -The method of equalizing transmission of a plurality of carrierchannels trans- 'mitted over or through the same medium,

-which consists in dividing the channels into such a number of groupsthat the highest4 frequency in any group shall be at least twice aslarge as the lowest frequency in the said group,'beating the frequenciesin two adjacent groups by the sum of the highest and lowest frequenciespresent inv both groups, selecting the differencel frequencies of thesaid'beating operation, Iand amplify-V ing the selected frequencies ineach group, the degree of amplification being in accordance with therelative position of the said frequencies in the frequency spectrum, andcombining the frequencies as-thus amplified.

6. Ina carrier signaling system, the combination with a terminal circuitcomprising a plurality of branches, each having a source of carriercurrent, the frequency of which differs from that-of thel others, asource of.

signaling current to modulate the said carrier, al transmission circuitconnected with the vsaidvtermvinal. circuit and common to all of saidbranches,` and.V a repeater lcomprising two branches each having afilter, a modulatorand an amplifier, and a source of/beatingoscillations, the frequency beingl the same for both branches and equaltothe sumar. the lowest frequency and the highest'` frequency present inall channels.

7.T,he,method of equalizing the'transmission' equivalents of a pluralityof carrier channels which consists in transmitting a.

plurality of channels of different frequencies, separating the saidchannels into a plurality of groups, the number of which'will be suchthat the lowest frequency in any group shall be equal to or greater thanhalf of the highest frequency in that group, separating the channels `ineach groupv into two sub-groups and separately beating the channels ineachsub-group with a beating frequency equal to the sum of the lowestand t-he'highest frequency in each vpair of sub-A groups, selecting thedifference frequencies resulting from'each beating operation,ameplifying and transmitting the selected fre-4 quencies.

8.l In a carrier signaling-system, the combination with a transmissionline of a repeater inserted between sections thereof, a f

source of a plurality of channels connected ywith the said line, saidrepeater comprising a plurality of branch circuits connected with thesaid line having mutually exclusive filters, one adapted to pass thelower range of frequencies and the other the higher range,

each branch having a modulator and a filter lconnected with the outputthereof,` and a source of beat-ing oscillations connected with the inputsides 'of bothl modulators, thefrequency of the'said beatingoscillations being equal to the sum of the lowest and the highestfrequencies in all channels.

9. In a carrier signaling system, the combination with atransmissionline of a repeater inserted between sections thereof, a source of apluralityof channels connectedl Dwith the said line, saidl repeatercomprising a plurality of branch circuits connected with the said linehaving mutually exclusive filters, one adapted to pass the lower rangeof frequencies and the other the higher range, each branch having l'amodulator and a filter connected with the output thereof, a source ofbeating oscillations connected with the input sides of both modulators,the frequency of the said beating oscillations being equal to the sum ofthe lowest and the highest frequencies in all channels, and meansconnected with eachlbra'nch circuit to amplify the frequenciestransmitted by the respective'flters. l

Iny testimony whereof, I have signed my name to `this specification'this 29th day of December, 1925.

EsTILL IQ GREEN.

